This experiment is a standard synthesis lab in which organic reactions are used in the construction of new organic molecules. One type of synthesis experiment uses halogenation. Halogenation is the addition of halogen atoms to a π-bond system, the bond breaks and a haloalkane is formed. This experiment uses bromination , the specific name of halogenation of (with) bromine. In order to for bromination to occur bromine must first be generated. This is done in situ through the oxidation of hydrobromic acid and hydrogen peroxide. Once generation is accomplished the available bromine can be brominated. The in-situ process is done to eliminate that risk of direct handling of bromine. Ethanol is used as the solvent and the oxidation of hydrobromic acid with hydrogen peroxide act as the reagent. These chemicals are choosen for their lower risk and environmentally friendly qualities. The effect of bromination of (E)-stilbene result is the formation of 1,2-dibromo-1.2-diphenylethane (dibromostilbene).
Reaction 1: shows the reagents hydrobromic acid and hydrogen peroxide generating bromine via the in situ method.
[from Doxsee, K.M. and Hutchison, J.E. Green Organic Chemistry ]
Nice job on the intro.
Pocedure: [adapted from Doxsee, K.M. and Hutchison, J.E. Green Organic Chemistry ]
Prepare a hot water bath using a shallow dish or beaker on a stirrer/hot plate.
Place a magnetic stir bar, 0.5 g of E-stilbene, and 10 mL of ethanol in a 100-mL round-bottom flask. Fit the flask with a water cooled reflux condenser.
Clamp the flask at the lowest joint so that it may be heated and stirred in the hot water bath. Stir while heating the mixture to reflux--the majority of the solid should dissolve.
Slowly add 1.2 mL of concentrated 48% aqueous HBr. This addition will probably cause some of the stilbene to precipitate, but if you continue heating and stirring it should redissolve. Go on to the next step even if some solid is present.
Measure out 0.8 mL of 30% hydrogen peroxide from the communal burette and add it drop-wise to the reaction mixture. The initially colorless solution should change to a golden-yellow color.
Continue to stir under reflux until the yellow color fades and the mixture becomes cloudy white (approximately 20 minutes).
Remove the flask from the hot water bath and allow it to cool to room temperature. Carefully adjust the pH of the solution to pH 5 to 7 using concentrated aqueous sodium bicarbonate (NaHCO3) (you don't have to dip the pH paper into the mixture-just use your spatula to touch the pH paper with a little of the liquid from the mixture). It may take very little NaHCO3 to neutralize the acid.
Cool the mixture further using an ice bath. Isolate the product by vacuum filtration.
Determine the mass of the product and measure it melting point (literature value: mp 241 °C)
Data:
Initial measurements:
10.0ml 95% ethanol (clear liquid)
0.503g stilbene (white powdery solid)
1.2ml 48% HBr (clear liquid with orange tint)
0.8ml 30% H2O2 (clear liquid)
The mixture of ethanol and stilbene produced a clear liquid. When the HBr was added to it, the mixture took on a milky/opaque look with a slight orange tint. When the H2O2 was added the mixture became bright yellow, then bright orange/yellow, then turning darker orange and then gradually fading to a milky pale yellow. The mixture separated into two layers with the top being a bright orange transparent liquid and the bottom layer being a cloudy yellow liquid. After cooling, the mixture separated into two distinct layers with the bottom layer being cloudy white with a hint of yellow and the top clear with a hint of gold.
4ml + 10 drops of saturated NaHCO3 (to reduce acidity) The two separate layers combined into one.
49.614g empty watch glass
50.230g watch glass with recovered product
0.616g net weight of recovered product (white powdery substance)
Melting Point Data
Temperature (in degrees Celsius)
Color and state of substance
26.7
White and powdery
197.3
Light caramel
207.2
Dark caramel/ brownish
211.7
Begin melting
228.9
Darker caramel/amber brown and more liquid
237.7
Dark amber brown and all thick viscous liquid much like molasses
good with the data: all the info is here without a lot of extra stuff.
Results:
At first the aqueous hydrobromic acid was transparent with a slight hint of dark orange color. After adding 0.8ml of 30% hydrogen peroxide, the mixture turned instantly to bright yellowish. When more Hydroxide peroxide was added the color darkened to orange-yellowish . The mixture separated into two layers, bottom layer was cloudy yellowish and the top layer was a bright clear orange liquid. After heating for 18 min the mixture turned white and divided into two layers, one layer was translucent and the other layer was white opaque. The pH of the solution after the addition of NaHCO3 (10drops and 4ml =70 drops) was determined to be 6 because it turned litmus paper the yellow color corresponding to a pH of 6 on the litmus color scale.
0.616g of a white crystal solid was collected, When taken the melting point of the crystals: the first color change to tan happened at 198.3 °C, become darker caramel at 208.9 °C (color change indicates a chemical reaction). At the average temperature between 213.4 °C and 235.83 °C it metled (spellcheck) into a caramel liquid (m.p)
Formula Mass:
stilbene=C14H12= 12.001 x 14 + 1.0079 x 12= 180.248 of stilbene
dibromostilbene=C14H12Br2= 12.001x14+1.0079 x12 +79.904 x 2 = 340.056g dibromostilbene
0.503g stilbene x 1 mol stilbene x 340.056g dibromostilbene =0.949 grams of dibromostilbene
180.248 g stilbene 1 mol dibromostilbene
.616 grams of dibromostilbene (experimental yield) x 100 = 65.0 % yield
.949 grams of dibromostilbene (theoretical yield)
calculations ok, and ok on the sig figs too!
Conclusion and Analysis:
The intentions of this experiment were to demonstrate the bromination of E-stilbene forms dibromostilbene. In addition a comparison of the product yield to the theoretical yield and the products purity were concluded. The product yield was lower than theoretical yield which is typically 90%, 0.616 g of dibromostilbene was produced and recovered in the experiment. which is just 65.0% of the theoretical yield.
The melting point of the final product was lower than the accepted value (241 °C) This indicates that the product (dimbromostilbene ) was not completely pure. However the m.p was close. Another reason for the lower melting point could be attributed to the individual observation was determing the exact temperature the product turned color. Knowing that color indicates a change in the chemical composition of a substance it is important to report on the temperature as the shades of caramel and brown darkened. The importance of this may be missed if the individual is focused on watching the product form the first liquid drop.
This report earned the following scores for: format (2/2) style (1.5/2) data (3/3) quality of result (1/1) quality of reported data (1/1) conclusion (2/2) error (1/1) post-lab question (2/2) for a total of 13.5/14.
Green Bromination of Stilbene
Introduction:
This experiment is a standard synthesis lab in which organic reactions are used in the construction of new organic molecules. One type of synthesis experiment uses halogenation. Halogenation is the addition of halogen atoms to a π-bond system, the bond breaks and a haloalkane is formed. This experiment uses bromination , the specific name of halogenation of (with) bromine. In order to for bromination to occur bromine must first be generated. This is done in situ through the oxidation of hydrobromic acid and hydrogen peroxide. Once generation is accomplished the available bromine can be brominated. The in-situ process is done to eliminate that risk of direct handling of bromine. Ethanol is used as the solvent and the oxidation of hydrobromic acid with hydrogen peroxide act as the reagent. These chemicals are choosen for their lower risk and environmentally friendly qualities. The effect of bromination of (E)-stilbene result is the formation of 1,2-dibromo-1.2-diphenylethane (dibromostilbene).
Reaction 1: shows the reagents hydrobromic acid and hydrogen peroxide generating bromine via the in situ method.
[from Doxsee, K.M. and Hutchison, J.E. Green Organic Chemistry ]
Nice job on the intro.
Pocedure: [adapted from Doxsee, K.M. and Hutchison, J.E. Green Organic Chemistry ]
Prepare a hot water bath using a shallow dish or beaker on a stirrer/hot plate.
Place a magnetic stir bar, 0.5 g of E-stilbene, and 10 mL of ethanol in a 100-mL round-bottom flask. Fit the flask with a water cooled reflux condenser.
Clamp the flask at the lowest joint so that it may be heated and stirred in the hot water bath. Stir while heating the mixture to reflux--the majority of the solid should dissolve.
Slowly add 1.2 mL of concentrated 48% aqueous HBr. This addition will probably cause some of the stilbene to precipitate, but if you continue heating and stirring it should redissolve. Go on to the next step even if some solid is present.
Measure out 0.8 mL of 30% hydrogen peroxide from the communal burette and add it drop-wise to the reaction mixture. The initially colorless solution should change to a golden-yellow color.
Continue to stir under reflux until the yellow color fades and the mixture becomes cloudy white (approximately 20 minutes).
Remove the flask from the hot water bath and allow it to cool to room temperature. Carefully adjust the pH of the solution to pH 5 to 7 using concentrated aqueous sodium bicarbonate (NaHCO3) (you don't have to dip the pH paper into the mixture-just use your spatula to touch the pH paper with a little of the liquid from the mixture). It may take very little NaHCO3 to neutralize the acid.
Cool the mixture further using an ice bath. Isolate the product by vacuum filtration.
Determine the mass of the product and measure it melting point (literature value: mp 241 °C)
Data:
Initial measurements:
10.0ml 95% ethanol (clear liquid)
0.503g stilbene (white powdery solid)
1.2ml 48% HBr (clear liquid with orange tint)
0.8ml 30% H2O2 (clear liquid)
The mixture of ethanol and stilbene produced a clear liquid. When the HBr was added to it, the mixture took on a milky/opaque look with a slight orange tint. When the H2O2 was added the mixture became bright yellow, then bright orange/yellow, then turning darker orange and then gradually fading to a milky pale yellow. The mixture separated into two layers with the top being a bright orange transparent liquid and the bottom layer being a cloudy yellow liquid. After cooling, the mixture separated into two distinct layers with the bottom layer being cloudy white with a hint of yellow and the top clear with a hint of gold.
4ml + 10 drops of saturated NaHCO3 (to reduce acidity) The two separate layers combined into one.
49.614g empty watch glass
50.230g watch glass with recovered product
0.616g net weight of recovered product (white powdery substance)
Melting Point Data
much like molasses
Results:
At first the aqueous hydrobromic acid was transparent with a slight hint of dark orange color. After adding 0.8ml of 30% hydrogen peroxide, the mixture turned instantly to bright yellowish. When more Hydroxide peroxide was added the color darkened to orange-yellowish . The mixture separated into two layers, bottom layer was cloudy yellowish and the top layer was a bright clear orange liquid. After heating for 18 min the mixture turned white and divided into two layers, one layer was translucent and the other layer was white opaque. The pH of the solution after the addition of NaHCO3 (10drops and 4ml =70 drops) was determined to be 6 because it turned litmus paper the yellow color corresponding to a pH of 6 on the litmus color scale.
0.616g of a white crystal solid was collected, When taken the melting point of the crystals: the first color change to tan happened at 198.3 °C, become darker caramel at 208.9 °C (color change indicates a chemical reaction). At the average temperature between 213.4 °C and 235.83 °C it metled (spellcheck) into a caramel liquid (m.p)
Formula Mass:
stilbene=C14H12= 12.001 x 14 + 1.0079 x 12= 180.248 of stilbene
dibromostilbene=C14H12Br2= 12.001x14+1.0079 x12 +79.904 x 2 = 340.056g dibromostilbene
0.503g stilbene x 1 mol stilbene x 340.056g dibromostilbene =0.949 grams of dibromostilbene
180.248 g stilbene 1 mol dibromostilbene
.616 grams of dibromostilbene (experimental yield) x 100 = 65.0 % yield
.949 grams of dibromostilbene (theoretical yield)
calculations ok, and ok on the sig figs too!
Conclusion and Analysis:
The intentions of this experiment were to demonstrate the bromination of E-stilbene forms dibromostilbene. In addition a comparison of the product yield to the theoretical yield and the products purity were concluded. The product yield was lower than theoretical yield which is typically 90%, 0.616 g of dibromostilbene was produced and recovered in the experiment. which is just 65.0% of the theoretical yield.
The melting point of the final product was lower than the accepted value (241 °C) This indicates that the product (dimbromostilbene ) was not completely pure. However the m.p was close. Another reason for the lower melting point could be attributed to the individual observation was determing the exact temperature the product turned color. Knowing that color indicates a change in the chemical composition of a substance it is important to report on the temperature as the shades of caramel and brown darkened. The importance of this may be missed if the individual is focused on watching the product form the first liquid drop.
This report earned the following scores for: format (2/2) style (1.5/2) data (3/3) quality of result (1/1) quality of reported data (1/1) conclusion (2/2) error (1/1) post-lab question (2/2) for a total of 13.5/14.
Well done!